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kn KLEINFFLDER t I We do not know of groundwater contamination issues at the project site at this time. No underground storage tanks are known to exist on the site and no gas stations are located adjacent to the site. The potential sources of nitrate in the project area include the grazing of cattle and horses, existing septic systems for single-family housing located in the project area; and any fertilizers, pesticides, and herbicides that may be used for agricultural purposes in the area. After the parcels cels are developed, we anticipate that the on-site sources of nitrate p P trate will � i include the septic systems, lawn fertilizers, and potentially horses grazing an theP arcels. 5. SOIL PROFILE �`' The subsurface conditions at the site were explored on June 3, 2005, by drilling a boring in f 4 each of the two lots to a depth of about 25 feet below existing grade. The borings were drilled using a Simco 2400 truck-mounted drill rig equipped with 4%-inch O.D. solid-stem auger. The approximate location of the test borings and dimensions from reference points are presented on the Plate 1. The soils observed were visually classified according to the Unified Soil Classification System (see Plate 3). a Based on our findings, the subsurface soils encountered in our borings consisted of fine-grained clayey sand to depths ranging from about 3 to 3 % feet below the existing site grade, underlain by strata of weakly cemented silty sand, sandy clay, and sandy silt to depths ranging from about 1 I % to 14 feet below the existing site grade. These soils were underlain by clayey sand with varying amounts of gravel to the maximum depth explored. The soils encountered were generally cemented and very difficult to drill through. A key to the Logs of Borings is presented on Plate 4. Detailed descriptions of the subsurface conditions encountered during our field investigation are presented on the Logs of Borings, Plates 5 and 6. The Soil Survey of San Joaquin County, California published by the U.S. Department of Agriculture, Soil Conservation Service (1992) refers to the near-surface soil within the project area as belonging to the Exeter soil series (Map Symbol 157). This soil is described as having "severe" percolation characteristics for septic tank absorption due to slow percolation and cemented pan. Other attributes are given in the table below: a R Ma■H■ _ �,Ava><lable Water Capacity a ,; r ante -•• 7 �s �',� i' y'14 O 9 i TAamVTr `t j ...° ,SBS mbol Soil Name e� .;._ inch stench F b.eE H Content ereent 157 Exeter 0.10-0.17 6.1 - 7.8 0- 1 6. PERCOLATION TESTING Shallow and deep percolation test holes were installed at the two lots on May 27, 2005 using a drill rig equipped with a 5-inch diameter auger. The approximate percolation test locations are presented on Plate 1. Following drilling, the sides of the holes were scored, and significant loose material was removed from the bottom of the holes. Test holes were prepared in # 57556.GO1/ST05ik687 June 10,2005 OO 2005 Kleinfelder,Inc. Page 3 of 5 11